guest blogger john hare
A recent discussion mentioned that some ELVs are launching with a T/W ratio of 1.15 or less. An ongoing discussion concerns the cost and limitations of launch pads for them. Space advocates like us would mostly like a wider variety of launch locationsÂ than the fixed launch pad facilities allow. Using available runways is a popular thought. It might be possible to dispense with the vertical launch pads, save money,Â and gain a little performance in the bargain.
It has been suggested many times that a launch sled would benefit HTHL RLVs.Â It seems possible that a launch sled set up might assist almost unmodified current ELVs. The flame containment of vertical launch could be exchanged for a few hundred feet of relatively inexpensive runway flame protection. The vehicle could accelerate at 8-9 meters per second instead of 1.5 in the initial 20 or so seconds. The ELV could abort if a problem is discovered in the first 15 seconds of full thrust.
A small ski ramp used in the same manner as the small British aircraft carriers for Harriers could start the turn vertical at the end of the runway. TVC could complete the turn as the sled dropped off keeping most of the velocity gained in the horizontal. The sled would provide structural support for the relatively fragile stack until it is in a stable trajectory. Considering the weight of the sled, the stack could accelerate to 160 m/s in the first 20 seconds instead of 30 m/s in a vertical launch. While there would be losses in the turn, net gain should be over 100 m/s for the stage. At the sharp end, this is somewhat useful. Canard wings at the front of the sled could assist the vertical maneuver.
Justification for the cost of this system could only be if it was weighed against building a new launch pad. If you have an existing one, or your vehicle doesn’t require a pad in the first place, the expense wouldn’t be justified. The development cost of a new way of launching could also be prohibitive.
Launch pad cost, launch pad availability, abort options, and slight performance gain could make this a concept worth consideration.